Abstract
X-ray free-electron laser oscillator (XFELO) is expected to be a cutting-edge tool for fully coherent x-ray laser generation, and undulator taper technique is well-known for considerably increasing the efficiency of free-electron lasers (FELs). In order to combine the advantages of these two schemes, FEL amplifier seeded by XFELO is proposed by simply using a chirped electron beam. With the right choice of the beam parameters, the bunch tail is within the gain bandwidth of XFELO, and lase to saturation, which will be served as a seeding for further amplification. Meanwhile, the bunch head which is outside the gain bandwidth of XFELO, is preserved and used in the following FEL amplifier. It is found that the natural ``double-horn'' beam current, as well as residual energy chirp from chicane compressor, are quite suitable for the new scheme. Inheriting the advantages from XFELO seeding and undulator tapering, it is feasible to generate nearly terawatt level, fully coherent x-ray pulses with unprecedented shot-to-shot stability, which might open up new scientific opportunities in various research fields.
Highlights
The successful operation of self-amplified spontaneous emission (SASE) [1,2] x-ray free-electron lasers (XFEL) [3,4,5,6] around the world have offered innovative approach for studying various areas such as atomic, molecular, and optical physics; condensed matter physics; mater in extreme conditions; chemistry and soft matter, and biology [7]
Using the parameters of Shanghai Coherent Light Facility (SCLF) as an example [28], we show that X-ray free-electron laser oscillator (XFELO) seeded amplifier is of potential for future XFEL facilities to significantly enhance FEL peak power, spectral brightness as well as output power stability
With the FEL gain of small current between two horns being ignored, the natural “double-horn” of electron beam is proved to be quite suitable for our scheme: the head horn is set to be outside the gain bandwidth and well-preserved for FEL amplifier; while the tail horn corresponding to maximum single pass gain is lasing inside the XFELO, and combine with the large distance 14 μm between the two horns would leads to relative small optimized energy chirp
Summary
The successful operation of self-amplified spontaneous emission (SASE) [1,2] x-ray free-electron lasers (XFEL) [3,4,5,6] around the world have offered innovative approach for studying various areas such as atomic, molecular, and optical physics; condensed matter physics; mater in extreme conditions; chemistry and soft matter, and biology [7]. The preservation of temporal coherence and operation stability for external-seeding technique are still not clear in hard x-ray region [13,14,15] Another major goal of XFEL development is to further enhance peak power and photon flux for increasing the resolution of x-ray imaging experiments [16,17]. Utilizing relativistic electron beam as gain medium and crystal as optical cavity mirrors, XFELO starts from spontaneous radiation and its spectra is purified during each Bragg reflection It is capable of generating stable, high repetition rate, fully coherent x-ray pulses [26,27]. Using the parameters of Shanghai Coherent Light Facility (SCLF) as an example [28], we show that XFELO seeded amplifier is of potential for future XFEL facilities to significantly enhance FEL peak power, spectral brightness as well as output power stability.
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